“Tetrahedral Chains and a Curious Semigroup: Doi:10.17398 2605-5686.34.1.99”. Extracta Mathematicae, vol. 34, no. 1, June 2019, p. 99-122, https://revista-em.unex.es/index.php/EM/article/view/2605-5686.34.1.99.